# `vminfp` — Vector Minimum Floating Point > **Category:** [VMX (Altivec)](../categories/vmx.md) · **Form:** [VX](../forms/VX.md) · **Opcode:** `0x1000044a` ## Assembler Mnemonics | Mnemonic | XML entry | Flags | Description | | --- | --- | --- | --- | | `vminfp` | `vminfp` | — | Vector Minimum Floating Point | | `vminfp128` | `vminfp128` | — | Vector128 Minimum Floating Point | ## Syntax ```asm vminfp [VD], [VA], [VB] vminfp128 [VD], [VA], [VB] ``` ## Encoding ### `vminfp` — form `VX` - **Opcode word:** `0x1000044a` - **Primary opcode (bits 0–5):** `4` - **Extended opcode:** `1098` - **Synchronising:** no | Bits | Field | Meaning | | --- | --- | --- | | 0–5 | `OPCD` | primary opcode (4) | | 6–10 | `VRT/VD` | destination vector register | | 11–15 | `VRA/VA` | source A vector register | | 16–20 | `VRB/VB` | source B vector register | | 21–31 | `XO` | extended opcode (11 bits) | ### `vminfp128` — form `VX128` - **Opcode word:** `0x180002c0` - **Primary opcode (bits 0–5):** `6` - **Extended opcode:** `704` - **Synchronising:** no | Bits | Field | Meaning | | --- | --- | --- | | 0–5 | `OPCD` | primary opcode (4 or 5) | | 6–10 | `VD128l` | destination low 5 bits | | 11–15 | `VA128l` | source A low 5 bits | | 16–20 | `VB128l` | source B low 5 bits | | 21 | `VA128H` | source A high bit | | 22 | `—` | reserved | | 23–25 | `VC` | optional VC / XO sub-field | | 26 | `VA128h` | source A middle bit | | 27 | `—` | reserved | | 28–29 | `VD128h` | destination high 2 bits | | 30–31 | `VB128h` | source B high 2 bits | ## Operands | Field | Role | Description | | --- | --- | --- | | `VA` | vminfp: read; vminfp128: read | Source A vector register. | | `VB` | vminfp: read; vminfp128: read | Source B vector register. | | `VD` | vminfp: write; vminfp128: write | Destination vector register. | ## Register Effects ### `vminfp` - **Reads (always):** `VA`, `VB` - **Reads (conditional):** _none_ - **Writes (always):** `VD` - **Writes (conditional):** _none_ ### `vminfp128` - **Reads (always):** `VA`, `VB` - **Reads (conditional):** _none_ - **Writes (always):** `VD` - **Writes (conditional):** _none_ ## Status-Register Effects _No condition-register or status-register effects._ ## Operation (pseudocode) ``` ; Pseudocode derives directly from the xenia-rs interpreter ; arm (see Implementation References). Operation semantics: ; - Read source operands from the fields listed under Operands. ; - Apply the arithmetic / logical / memory action described ; in the Description field above. ; - Write results to the destination register(s); update any ; status bits enumerated under Status-Register Effects. ; Consult the IBM AIX reference link under IBM Reference for ; canonical PPC-style pseudocode where xenia's expression is ; terse. ``` ## C Translation Example ```c /* C translation: the xenia-rs interpreter arm below in */ /* Implementation References is the authoritative semantic */ /* snapshot. Translate it line-by-line: */ /* - ctx.gpr[N] -> r[N] (or f[]/v[] for FPRs/VRs) */ /* - mem.read_u*/write_u* -> mem_read_u*_be / mem_write_u*_be */ /* - ctx.update_cr_signed(fld, v) -> update_cr_signed(fld, v) */ /* - ctx.xer_ca / xer_ov / xer_so -> xer.CA / xer.OV / xer.SO */ /* The Register Effects and Status-Register Effects tables above */ /* enumerate every side effect a faithful translation must emit. */ ``` ## Implementation References **`vminfp`** - xenia-canary XML: [`tools/ppc-instructions.xml` — search for `mnem="vminfp"`](../../xenia-canary/tools/ppc-instructions.xml) - xenia-canary emit: [`src/xenia/cpu/ppc/ppc_emit_altivec.cc:899`](../../xenia-canary/src/xenia/cpu/ppc/ppc_emit_altivec.cc#L899) - xenia-rs opcode: [`crates/xenia-cpu/src/opcode.rs:103`](../../xenia-rs/crates/xenia-cpu/src/opcode.rs#L103) - xenia-rs decoder: [`crates/xenia-cpu/src/decoder.rs:527`](../../xenia-rs/crates/xenia-cpu/src/decoder.rs#L527) - xenia-rs interpreter: [`crates/xenia-cpu/src/interpreter.rs:2137-2144`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L2137-L2144)
xenia-rs interpreter body (frozen snapshot) ```rust PpcOpcode::vminfp => { let a = ctx.vr[instr.ra()].as_f32x4(); let b = ctx.vr[instr.rb()].as_f32x4(); let mut r = [0f32; 4]; for i in 0..4 { r[i] = vmx::min_nan(a[i], b[i]); } ctx.vr[instr.rd()] = xenia_types::Vec128::from_f32x4_array(r); ctx.pc += 4; } ```
**`vminfp128`** - xenia-canary XML: [`tools/ppc-instructions.xml` — search for `mnem="vminfp128"`](../../xenia-canary/tools/ppc-instructions.xml) - xenia-canary emit: [`src/xenia/cpu/ppc/ppc_emit_altivec.cc:902`](../../xenia-canary/src/xenia/cpu/ppc/ppc_emit_altivec.cc#L902) - xenia-rs opcode: [`crates/xenia-cpu/src/opcode.rs:103`](../../xenia-rs/crates/xenia-cpu/src/opcode.rs#L103) - xenia-rs decoder: [`crates/xenia-cpu/src/decoder.rs:697`](../../xenia-rs/crates/xenia-cpu/src/decoder.rs#L697) - xenia-rs interpreter: [`crates/xenia-cpu/src/interpreter.rs:2145-2152`](../../xenia-rs/crates/xenia-cpu/src/interpreter.rs#L2145-L2152)
xenia-rs interpreter body (frozen snapshot) ```rust PpcOpcode::vminfp128 => { let a = ctx.vr[instr.va128()].as_f32x4(); let b = ctx.vr[instr.vb128()].as_f32x4(); let mut r = [0f32; 4]; for i in 0..4 { r[i] = vmx::min_nan(a[i], b[i]); } ctx.vr[instr.vd128()] = xenia_types::Vec128::from_f32x4_array(r); ctx.pc += 4; } ```
## Special Cases & Edge Conditions - **Per-lane IEEE min.** Four word lanes; `VD[i] = (VA[i] < VB[i]) ? VA[i] : VB[i]`. - **NaN propagation surprise.** Xenia uses `if a < b { a } else { b }`, so any NaN comparison evaluates false and the result is `VB`. The IBM manual specifies NaN-propagating min — i.e. NaN inputs should yield NaN. Hardware's `vminfp(NaN, x) = NaN` while xenia returns `x`. **Worth checking against `vmx.rs` for any future correctness fixes.** - **Sign of zero.** `vminfp(+0, -0)` returns `-0` in xenia (since `+0 < -0` is false → returns `b = -0`); hardware likely returns the negative zero too via the same comparator. - **`VSCR[NJ]` denormals.** With `NJ = 1` (Xenon default), denormal inputs are flushed to `±0` before comparison. - **No `VSCR[SAT]` change, no XER change, no exceptions.** - **Big-endian word lanes.** Lane 0 is the most-significant word. - **Aliasing legal.** `vminfp v3, v3, v4` clamps `v3` from above by `v4`. - **VMX128 sibling (`vminfp128`).** Identical comparator semantics with the extended encoding. ## Related Instructions - [`vmaxfp`](vmaxfp.md) — the per-lane maximum. - [`vcmpgtfp`](vcmpgtfp.md), [`vcmpgefp`](vcmpgefp.md) — separate compare-and-mask path. - [`vsel`](vsel.md) — combine masks with arbitrary alternatives. - [`vmaddfp`](vmaddfp.md) — fused multiply-add when the min is part of a polynomial. - [`vminsw`](vminsw.md) — integer-word min if the lanes are signed integers. ## IBM Reference - [AIX 7.3 — `vminfp` (Vector Minimum Floating Point)](https://www.ibm.com/docs/en/aix/7.3.0?topic=set-vminfp-vector-minimum-floating-point-instruction) - [IBM AltiVec Technology Programmer's Interface Manual, Chapter 5 — Floating-Point Min/Max](https://www.nxp.com/docs/en/reference-manual/ALTIVECPIM.pdf)